By Emery P. Dalesio

AP Business Writer

RALEIGH — A state appeals court should keep alive a five-year-old lawsuit because it increases the pressure on Duke Energy Corp. to clean up groundwater contaminated by its coal ash pits, environmental lawyers argued Thursday.

The Charlotte-based electricity utility admits coal ash has tainted underground water supplies but says the potentially toxic brew hasn’t harmed neighbors using water wells. Coal ash, the residue left after decades of burning coal to generate power, can contain toxic materials like arsenic and mercury.

One of the country’s largest electricity companies, Duke Energy is currently asking North Carolina utilities regulators to allow it to charge customers all costs associated with coal-ash cleanup, a price tag estimated at about $5 billion.

A Duke Energy lawyer told a trio of judges on the state Court of Appeals the lawsuit filed by the state’s environmental protection agency and joined by conservation groups should be dismissed.

The company is following deadlines set by a state law passed in 2014 mandating coal-ash disposal at 14 North Carolina power plants, and only that law can enforce the cleanup, Duke Energy lawyer Nash Long said. The lawsuit filed in 2013 seeks to force the company to stop polluting and clean up contaminated water sources.

The company was in court in part because Superior Court Judge Paul Ridgeway has refused to dismiss the lawsuit. Ridgeway has indicated he would review the remediation plan the state Department of Environmental Quality approves, then decide independently whether the agency is requiring enough from Duke Energy to clean up the pollution, Long said.

That could lead to the judge laying out facts describing the extent of groundwater pollution that coal ash has caused and how long Duke Energy has known about it.

“There is evidence we are going to present to the court … (offering) expert opinion as to where the contamination has come from, where it’s going,” said D.J. Gerken, an attorney for the Southern Environmental Law Center. “The court needs to hear that and make findings of fact.”

Duke Energy wants the lawsuit delayed and dismissed so that it can postpone cleaning up coal ash pollution at its power plants, Gerken said in an earlier court filing.

Long said Duke Energy lacks direction on how it must clean up groundwater pollution until DEQ approves the company’s remediation plan.

“Duke cannot start corrective action until that takes place,” Long said.

Judge Lucy Inman noted the conservation groups are arguing that keeping the lawsuit alive is valuable “because it’s necessary to light a fire under Duke” so it doesn’t stall cleaning up the pollution that’s lasted for decades.

The company last month agreed to pay an $84,000 penalty and work to stop potentially toxic waste from three coal-burning power plants from leaking into groundwater and nearby rivers under a deal with state regulators.

The agreement acknowledges the leaks from unlined, earthen basins into the adjoining Catawba and Broad rivers.